面试题 04.01. 节点间通路
class Solution 
{
private:
    vector<bool> visit;
    unordered_map<int,unordered_set<int>> gragh;
public:
    bool Dfs(int start,int end)
    {
        if(start==end)
        {
            return true;
        }

        if(visit[start])
        {
            return false;
        }

        visit[start]=true;

        for(auto& newstart : gragh[start])
        {
            if(Dfs(newstart,end))
                return true;
        }

        return false;
    }

    bool findWhetherExistsPath(int n, vector<vector<int>>& _graph, int start, int target) 
    {
        for(int i=0;i<_graph.size();i++)
        {
            gragh[_graph[i][0]].insert(_graph[i][1]);
        }

        visit = vector<bool>(n,0);

        return Dfs(start,target);
    }
};


596. 超过 5 名学生的课
# Write your MySQL query statement below
select
    class
from 
    Courses
group by
    class
having 
    count(*)>4